Plastic covered flexible waveguide formed from a metal coated dielectric layer

ABSTRACT

A flexible waveguide composed of a tube of noncircular cross section formed by overlapping opposite edges of a sheet, the sheet being a laminate formed of metal foil covered on one surface by a layer of flexible dielectric. The exterior of the tube is covered with additional flexible dielectric material which forms a relatively thick protective coating.

i 4 United States Patent Gissel [54] PLASTIC COVERED FLEXIBLE WAVEGUIDEFORMED FROM A I .METAL COATED DIELECTRIC LAYER [72] Inventor: I'IansGissel, Backnang'Wurtternberg, Germany TelefunlrenPatentverwertungsgesellschaft m.b.II., Ulm-Donau, Germany [22] Filed:Oct 28, 1969 [21] Appl.No.: 871,870

[73] Assignee:

[30] Foreign Application Priority Data Nov. 8, 1968 [52] ILS. Cl...333/95 R, 333/95 A, 29/600 I [51] Int.Cl [58] FieldofSearch ..II0lp3/14,H01p 11/00 333/95, 95 A; 174/109; 29/600, 29/601 [56] ReferencesCited UNITED STATES PATENTS Germany ..P 18 07 718.4

1451 Mar. 7, 1972 1 Primary Examiner-Herman Karl Saalbach AssistantExaminer-Wm. H. Punter Attorney-Spencer & Kaye [57] ABSTRACT A flexiblewaveguide composed of a tube of noncircular cross section formed byoverlapping opposite edges of a sheet, the sheet being a laminate formedof metal foil covered on one surface by a layer of flexible dielectric.The exterior of the tube is covered with'additional flexible dielectricmaterial which forms a relatively thick protective coating.

11 Claims, 3 Drawing Figures Patented March 7, 1972 Inventor Hans GisselJ BY %m-ew t aye,

ATTORNEYS.

PLASTIC COVERED FLEXIBLE WAVEGUIDE FORMED FROM A METAL COATED DIELECTRICLAYER BACKGROUND OF THE INVENTION This invention relates to waveguides,and more particularly to a flexible dielectric tube having a metallizedlayer on its interior surface to permit its use as a waveguide.

Prior art flexible waveguides have been made of corrugated metal tubescovered with an additional protective coating of a dielectric materialsuch as a plastic. These presented certain disadvantages. The corrugatedmetal tube was subject to corrosion and the waveguide was relativelyheavy. Moreover, the manufacturing expense for forming such a corrugatedtube was relatively great. In addition the corrugations impaired thetransmission properties of the waveguide.

SUMMARY OF THE INVENTION Among the objects of the present invention isthe provision of a waveguide which is free of the above-noted drawbacksin that it is inexpensive to manufacture, light in weight and has astructure which does not adversely affect the transmission properties ofthe waveguide.

Briefly stated, these and other objects of the present invention areachieved by forming a tube from a laminated sheet formed of a metal foilcovered with a dielectric layer. The opposite edges of the sheet areoverlapped with the metal foil forming the tube interior. The sheet isglued or welded at the points of overlap and the entire tube is thencovered with an additional protective coating of dielectricmaterial,such as plastic. The internal cross section of the tube is noncircular.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-sectional viewthrough a waveguide according to the present invention.

FIG. 2 is a perspective view, partly in section and partly broken away,of the waveguide of FIG. 1.

FIG. 3 is a cross-sectional view of a waveguide according to anotherembodiment of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings,a waveguide according to the present invention is formed with a sheet 1having opposite edges bent back upon itself to form a tube 2 having anapproximately elliptical inner cross section 4. The tube interior has amajor diameter d and a minor diameter d,. The edges are overlappedthrough a region C whose width is approximately one-quarter of thewavelength of the waves to be transmitted over the waveguide. Thelongitudinal seam 5 of the overlapped region is secured by a welded orglued joint 6.

Sheet 1 is formed of a metal foil layer In and a layer of dielectricmaterial lb. The metal foil may be of copper or aluminum and thedielectric material may be of polyethylene or polyisobutylene mixed withcarbon black or graphite. The relative thickness of the sheet layers issomewhat exaggerated in the drawing to more clearly show the structure.The exterior of the tube is covered with a protective coating 3 ofpolyvinyl chloride.

The protective coating 3 is secured to the tube 2 by gluing or welding.In the preferred embodiment the polyvinyl chloride may be sprayed on.The heat released as the polyvinyl chloride mass hardens may be used toweld the dielectric layer of the tube 2 and its metal foil in the regionof the seam 5. The exterior surface of coating 3 is of circular crosssection.

During fabrication, the sheet 1 is placed over a suitably shaped core toproduce the desired inner cross section for the waveguide and thedesired overlap. The waveguide can be easily manufactured in any desiredlength with the aid of conventional cable sheathing machines.

The thickness of the metal foil and of the other materials involved areprimarily selected so that the waveguide can be bent about desired radiior through desired torsion angles without undesirable buckling or otherdistortion when the guide is installed. From an electrical point of viewthe layer thickness of the foil should be a multiple of the penetrationdepth of the electromagnetic waves to be transmitted. This will sufficefor externally shielding the waveguide. For reasons of stability thethickness of the metal foil is always a multiple of the above-mentionedpenetration depth.

Unintended escape of electromagnetic energy from the interior of thewaveguide in the region of the overlap may be avoided by making theoverlap width C equal to approximately a quarter wavelength of the waveto be transmitted. Preferably the overlapping zone extends parallel tothe longitudinal axis of the waveguide and is arranged that it extendsapproximately perpendicular with the Hy vector of the guided waves. Thedielectric material lb may be enriched with a material which stronglydamps electromagnetic waves in order to prevent the escape ofelectromagnetic energy in this region.

Preferably this additive is concentrated in the region of the overlap.For this purpose graphite is added to the dielectric material lb with apercentage by volume of about 10-30 percent.

Referring now to FIG. 3, another embodiment of the invention is seen inwhich the inner cross section of the waveguide is rectangular withsharply rounded corners. This shape, or any other noncircular crosssection, may be fonned by using an appropriately formed core duringfabrication. Such shapes are useful for clear transmission of planepolarized waves.

This embodiment has a glued joint 6' securing the overlapped regionstogether and another glued joint 7 securing the protective coating 3 tothe tube 2.

In both embodiments of the invention the circular exterior of coating 3is particularly advantageous for attachment of the required fittings tothe waveguide. The waveguide according to either embodiment of thepresent invention is particularly suited for use in mobile stationswhere fast setup and takedown time for the antenna is required.

It will be apparent that there has been provided a waveguide which isinexpensive to manufacture, relatively light in weight and which isflexible and convenient to use.

For a particular embodiment of the invention intended to transmit wavesof a length of 5.9-6.5 MHz. a waveguide might have the followingdimensions:

Thickness of aluminum metal foil la 0.1 mm.,

thickness of sheet dielectric layer lb 3.5 mm.,

exterior diameter of coating 3 70 mm.,

major diameter d of interior of tube 2 43.6 mm.,

minor diameter d: of tube 2 25.9 mm.

The metal foil thickness is a multiple of the penetration depth of thewaves.

It will be understood that the above description of the presentinvention is susceptible to various modifications, changes andadaptations, and the same are intended to be comprehended within themeaning and range of equivalents of the appended claims.

I claim:

1. A waveguide comprising, in combination:

a. a tube of noncircular cross section formed of a laminated sheet of ametal foil layer which covers one surface of a layer of flexibledielectric material, said sheet extending back upon itself so thatopposite edge regions overlap for approximately one-quarter wavelengthwith the metal foil layer facing the interior of said tube, saidoverlapped regions of said laminated sheet being secured together, andextending parallel to the longitudinal axis of the waveguide andapproximately perpendicular to the Hy vector of the wave to betransmitted through said waveguide, said dielectric material containingmeans for damping transmitted electromagnetic waves at least in the areabetween said overlapped regions; and

b. a flexible dielectric coating covering the exterior of said tube andsecured thereto.

2. The combination defined in claim 1 wherein the inner cross section ofsaid tube is approximately elliptical.

3. The combination defined in claim 1 wherein said inner cross sectionis rectangular with rounded comers.

4. The combination defined in claim 1 wherein the outer cross section ofsaid flexible dielectric coating is of circular cross section.

5. The combination defined in claim 1 wherein said overlapped regionsare secured together and said flexible dielectric coating is secured tosaid tube by respective welded joints.

material is polyethylene.

9. The combination defined in claim 7 wherein said plastic material ispolyisobutylene.

10. The combination defined in claim 1 wherein said dielectric coatingis of polyvinyl chloride.

11. The combination defined in claim 1 wherein: said inner cross sectionof said tube is elliptical and the outer cross section of said flexibledielectric coating is circular; said overlapped regions are securedtogether and said flexible dielectric material is secured to theexterior of said tube by respective welded joints; said metal foil isaluminum; said dielectric material is a polyethylene mixed with carbon;and said flexible dielectric coating is of polyvinyl chloride.

I t i

2. The combination defined in claim 1 wherein the inner cross section ofsaid tube is approximately elliptical.
 3. The combination defined inclaim 1 wherein said inner cross section is rectangular with roundedcorners.
 4. The combination defined in claim 1 wherein the outer crosssection of said flexible dielectric coating is of circular crosssection.
 5. The combination defined in claim 1 wherein said overlappedregions are secured together and said flexible dielectric coating issecured to said tube by respective welded joints.
 6. The combinationdefined in claim 1 wherein said tube further comprises a glue jointsecuring said overlapped regions together and a glue joint securing saidflexible dielectric coating to the exterior of said tube.
 7. Thecombination defined in claim 1 wherein said dielectric material in saidlaminated sheet is a plastic mixed with carbon.
 8. The combinationdefined in claim 7 wherein said plastic material is polyethylene.
 9. Thecombination defined in claim 7 wherein said plastic material ispolyisobutylene.
 10. The combination defined in claim 1 wherein saiddielectric coating is of polyvinyl chloride.
 11. The combination definedin claim 1 wherein: said inner cross section of said tube is ellipticaland the outer cross section of said flexible dielectric coating iscircular; said overlapped regions are secured together and said flexibledielectric material is secured to the exterior of said tube byrespective welded joints; said metal foil is aluminum; said dielectricmaterial is a polyethylene mixed with carbon; and said flexibledielectric coating is of polyvinyl chloride.